Fix devtools bugs Fix a spurious layout test failure

Source/core/inspector/InspectorDebuggerAgent.h

 /*
  * Copyright (C) 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010-2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 182 matching lines @@
     void removeAsyncCallTrackingListener(AsyncCallTrackingListener*);
 
     // PromiseTracker::Listener
     void didUpdatePromise(InspectorFrontend::Debugger::EventType::Enum, PassRefPtr<TypeBuilder::Debugger::PromiseDetails>) final;
 
     // If behavior is broken, check to make sure we call this agent whenever we
     // call v8DebuggerAgent. Correct code flow is to call the dartAgent and if
     // it returns a value, don't call the v8Agent. The v8Agent has no idea the
     // dartAgent exists but the dartAgent was built with the knowledge that
     // there could be other agents around.
-    DartInspectorDebuggerAgent* dartAgent() { return 0; }
+    virtual DartInspectorDebuggerAgent* dartAgent() { return 0; }
 
 protected:
     InspectorDebuggerAgent(InjectedScriptManager*, v8::Isolate*);
 
     virtual void startListeningV8Debugger() = 0;
     virtual void stopListeningV8Debugger() = 0;
     virtual void muteConsole() = 0;
     virtual void unmuteConsole() = 0;
     InjectedScriptManager* injectedScriptManager() { return m_injectedScriptManager; }
     virtual InjectedScript injectedScriptForEval(ErrorString*, const int* executionContextId) = 0;
@@ skipping 101 matching lines @@
     int m_currentAsyncOperationId;
     bool m_pendingTraceAsyncOperationCompleted;
     bool m_startingStepIntoAsync;
     V8GlobalValueMap<String, v8::Script, v8::kNotWeak> m_compiledScripts;
 };
 
 } // namespace blink
 
 
 #endif // InspectorDebuggerAgent_h